First of all, a frame structure of a wireless communication system will be described with reference to FIG. 1. FIG. 1 is a diagram illustrating a frame structure of a long term evolution (LTE) system. As shown in FIG. 1, one frame includes ten subframes, each of which includes two slots. The time required to transmit one subframe will be referred to as a transmission time interval (hereinafter, referred to as “TTI”). For example, one subframe may be 1 ms, and one slot may be 0.5 ms.
One slot includes a plurality of orthogonal frequency division multiplexing (OFDM) symbols. The OFDM symbols may be referred to as SC-FDMA symbols or symbol duration.
One slot includes seven or six OFDM symbols in accordance with a length of cyclic prefix (hereinafter, referred to as “CP”). The LTE system includes a normal CP and an extended CP. One slot includes seven OFDM symbols if a normal CP is used, while one slot includes six OFDM symbols if an extended CP is used. The extended CP is used if delay spread is great.
In the wireless communication system, various types of subframes may be defined. For example, the LTE-A system may include Rel-8 subframes, relay subframes, multicast broadcast single frequency network (MBSFN) subframes and Rel-10 subframes.
The Rel-10 subframes may be regarded as the MBSFN frames to a Rel-8 mobile station, and a PDSCH of a Rel-10 mobile station may be transmitted through an MBSFN frame. A PDCCH structure is uniform regardless of types of subframes. A multicast channel uses the extended CP.
According to the related art, a CP length has been determined in accordance with a cell. For example, in case of a large-sized cell, since the distance between a base station and a mobile station may be long, the large-sized cell uses the extended CP, whereas a small-sized cell uses the normal CP. In other words, if a CP length is determined per cell, subframes in a frame of one cell use the CP of one length.
Even in case of the large-sized cell, since the mobile station located near the base station has small delay spread, it may transmit and receive data without any problem by using the normal CP. However, according to the related art, since the CP length is determined per cell, a problem occurs in that resource waste is caused due to the CP of the same length applied to subframes allocated to all the mobile stations within a cell.